Consumer camcorders which include the capability of recording analog motion and/or still images on 8mm or VHS videotape have been developed by a number of companies. Motion images are recorded in the same manner as in any standard camcorder. These cameras include a single chip charge coupled device (CCD) sensor having a color filter array that provides a spatially color-sampled image. To record still images, the user pushes a "still capture" button at the desired instant. The image obtained from the CCD sensor is temporarily stored in a digital memory. The image is then read from the memory and recorded onto the videotape. Some camcorders include color liquid crystal displays (LCD), which are also spatially color-sampled devices. Some are relatively large, for example, ranging from approximately 2.5" to 4" in diagonal. Such a display is used, instead of a normal eyepiece viewfinder, to allow the user to properly frame the subject and view the images as they are being recorded. It is also used to view the recorded images as the videotape is played back.
FIG. 1A shows a typical color LCD display, in which the liquid crystal material is trapped between an upper glass plate 1 and a lower glass plate 2. The upper plate 1 has a common transparent electrode 3 and an array 4 of color filters surrounded by a black mask 5. The lower plate 2 includes an array 6 of transparent pixel electrodes juxtaposed underneath the array 4 of color filters. Individual pixel electrodes are activated via thin film transistors (TFT) 7 that are controlled from a video signal on the source lines 8 and a scanning signal on the gate line 9. The LCD display includes the usual polarizer layers (not shown) on the glass plates 1 and 2, such that activation of selected transparent pixel electrodes allows light to pass through the corresponding color filters and reflect to the viewer, thereby creating a color image. A typical LCD display such as the Epson LB 2F-BC00, manufactured by Seiko-Epson Company, Japan, has about 240 lines of pixels and about 300 pixels per line, with an image aspect ratio of 4:3. Such an aspect ratio allows the entire area of the image obtained from the 4:3 aspect ratio NTSC format CCD sensor to be displayed on the LCD screen, so that the LCD screen composition will be the same as the image that is recorded by the camcorder NTSC format recorder, for later display on an NTSC format television display. Note that because the LCD has only 240 lines of pixels, the interlaced NTSC signal is displayed using a "repeat field" technique, where both the odd and even fields from the NTSC format sensor are displayed using the same lines of pixels on the LCD. This LCD, like most commercially available LCDS, has "rectangular" pixels, rather than square pixels, where the distance between pixels in the horizontal direction is for example 2/3 the distance in the vertical direction. The LCD pixels are overlaid with a diagonal RGB stripe pattern as shown in FIG. 1B.
In camcorders, the processing for both the still images and the motion images is identical. Such processing is normally implemented by hardwired analog integrated circuits, although camcorders which use digital image processing integrated circuits have been produced. Such camcorders convert the signal from the CCD sensor into an NTSC composite or component format signal, which is provided to a video recording subsystem or a video output jack. The color LCD display includes circuitry to decode the NTSC composite or component signal back into spatially subsampled RGB signals to drive the individual RGB pixels on the LCD sensor.
In a system oriented toward still photography, and in particular a digital still system, it would be desirable to avoid the necessity of generating an NTSC format signal in order to reduce the complexity of the required circuitry. In a totally digital system, that is, both the recording and display channels are digital, it is further desirable to minimize incompatibility between the channels. The problem is to achieve these objective in an architecture that minimizes cost and complexity and maximizes user handling.